title: On the mechanism and selectivity of the combined C-H activation/Cope rearrangement.
abstract: The combined C-H activation/Cope rearrangement (CHCR) is an effective C-H functionalization process that has been used for the asymmetric synthesis of natural products and pharmaceutical building blocks. Up until now, a detailed understanding of this process was lacking. Herein, we describe a combination of theoretical and experimental studies that have resulted in a coherent description of the likely mechanism of the reaction. Density functional studies on the reactions of rhodium vinylcarbenoids at allylic C-H sites demonstrate that the CHCR proceeds through a concerted, but highly asynchronous, hydride-transfer/C-C bond-forming event. Even though most of the previously known examples of this process are highly diastereoselective, the calculations demonstrate that other transition-states and stereochemical outcomes might be possible by appropriate modifications of the reagents, and this was confirmed experimentally. The calculations also indicate that there is a potential energy surface bifurcation between CHCR and the competing direct C-H insertion.
authors.affiliation: Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia 30322, USA.
authors.forename: Jørn H
authors.initials: JH
authors.lastname: Hansen
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Gregg
authors.forename: Stephanie R
authors.initials: SR
authors.lastname: Ovalles
authors.forename: Yajing
authors.initials: Y
authors.lastname: Lian
authors.forename: Jochen
authors.initials: J
authors.lastname: Autschbach
authors.forename: Huw M L
authors.initials: HM
authors.lastname: Davies